To my understanding, Both Chandra & Puru has been with IR since the very beginning (early 80's). Puru is a great percussionist,(Basically Drums). Most of the early nos of IR have had his solid contribution.
R.Chandrasheakar, who is the brother of Puru is basically a Key board player. He is also great at computerized musics & handling of softwares such as Cakewalk. I heard that he was among one who assisted IR even in Hey Ram. I think he is serving as the president of Tamil Nadu Music Association(you can see his posting in this forum).
Just listen to the music of Priya,HTNI etc, to feel their great work.